Ocean-bottom seismograph tomographic experiments-a consideration of acquisition geometries vs. resources

Abstract

Summary Over the last 20–30 yr numerous seismic images of the Earth's crust have revealed details of its gross structure, including intra‐crustal layering, the geometry of that layering and its composition. As more and higher quality studies are undertaken it is becoming apparent that identified structures have a greater degree of 3‐D variability than first anticipated. Thus, the methodology of crustal imaging by seismic means has also developed into the third dimension with a tomographic approach now being widely adopted, particularly so in the marine environment. Such surveys not only focus on mapping the finer scale 3‐D structural variability, they also aim to achieve sufficient density of azimuthal coverage and resolution to address preferential orientation patterns of features such as porosity, fracturing and faulting. Recent developments in technology, and consequently cheaper construction and deployment costs of instruments, have resulted in an expansion in the number of instruments available in ocean‐bottom seismometer pools. Consequently, individual experiments are being designed to accommodate the maximum number of instruments available and this, coupled with dense grids of shot profiles, significantly impacts on survey cost. In this paper we consider a variety of approaches to achieving the best resolution of detail for minimal associated cost of acquisition, and for instrument pools of various sizes. A number of different geometries are compared, including example grid designs in current use. Comparison of resolution tests and relative costings for a range of acquisition geometries suggest that, if instrument numbers and/or funds are limited, the most cost effective ways of achieving the desired target resolution may be by (1) shooting additional shot profiles at the expense of deploying more instruments and (2) multiple, overlapping deployments of a small geometry, tailored in shape to the target structure and depth.

The Correction of Shot and OBS Position in the 3D Seismic Experiment of the SW Indian Ocean Ridge

“…Getting adequate and precise phase information is critical to a final velocity structure during the data processing. In addition, the OBSs' release points and shooting lines should be fully considered and designed in order to make all OBSs record reflected and refracted signals from the whole lithosphere [10] .…”

Automated Seismic Acquisition Geometry Design for Optimized Illumination at the Target: A Linearized Approach

“…Further research is required for a global optimization algorithm incorporating such a constraint. methodology and the parameterization provide interesting opportunities in designing the location of ocean-bottom seismometers for crustal imaging purpose [37], or finding an optimum distribution of an earthquake monitoring network [38]. It requires the knowledge of the geological overburden, the location of the hypocenter, and the earthquake mechanism.…”

Crust and Lithospheric Structure - Active Source Studies of Crust and Lithospheric Structure

“…The modeling and inversion algorithms discussed later can be used to help design the optimum survey geometry given particular instrument resources and anticipated geologic structures (e.g., Peirce and Day, 2002).…”